Fig 3. Deletion of SPI-1 restores motility upon HilD induction.

(A) Swimming motility of the control, hilD↑ and various SPIs/adhesins mutant strains in soft-agar swim plates was monitored at 37°C for 3.5 h in absence (upper panel) or presence (lower panel) of 100 ng/ml AnTc to induce HilD production. Diameters of swimming halos were measured and normalized to the control strain (left). Representative swimming halos of the analysed mutants in absence (upper panel) or presence (lower panel) of AnTc are shown (right). Data from five biological replicates are shown as individual data points. Horizontal bars (red) represent the calculated mean of biological replicates. Statistical significances were determined using a two-tailed Student’s t-test (***, P < 0.001; **, P < 0.01; *, P < 0.05; ns, P > 0.05). (B) Single-cell swimming velocities of the control, hilD↑ and various SPIs/adhesins mutant strains in absence or presence of AnTc to induce HilD production. Individual data points represent the averages of the single-cell velocities of independent experiments. Violin plots represent data values from at least 700 analysed single-cell tracks. Horizontal bars (bold) represent the mean of the calculated average velocities of three independent experiments. The error bars represent the standard error of mean and statistical significances were determined using a two-tailed Student’s t-test (***, P < 0.001; **, P < 0.01; ns, P > 0.05). Strains analysed were TH437 (control), TH17114 (hilD↑), EM12479 (hilD↑ ΔSPI-1), EM13020 (hilD↑ ΔSPI-2), EM12354 (hilD↑ ΔSPI-4), EM13021 (hilD↑ ΔSPI-5) and EM12648 (hilD↑ Δ12 ΔcsgA). hilD↑: strain expressing hilD under an inducible promoter. Δ12: strain deleted for 12 chaperone-usher fimbrial operons. AnTc: anhydrotetracycline.